What happened
On January 15, 2015, a Boeing 787-8 operating within the Warsaw Flight Information Region (FIR EPWW) was climbing through various flight levels. After initially being cleared to flight level (FL) 320, the crew received clearance to continue climbing to FL 380. This clearance was designed to maintain separation from another aircraft traveling on FL 360.
Approximately 11 minutes before a potential conflict could occur, air traffic control (ATC) instructed the crew to expedite their climb to cross FL 370. The crew acknowledged this instruction. However, as the aircraft reached FL 348, the crew ceased the climb to prioritize maintaining airspeed, but they failed to notify ATC of this change in performance. At the time, the sector was heavily congested with over 20 aircraft. Four minutes before the potential conflict, ATC identified that the aircraft was not reaching the required altitude and subsequently instructed the crew to execute a turn to ensure necessary separation.
The investigation
The investigation, conducted by the aircraft operator's commission, examined the sequence of events leading to the loss of separation. The inquiry focused on the interaction between the flight crew and ATC, the performance of the Boeing 787-8 during the expedited climb, and the effectiveness of the instructions issued by the controller.
Findings
- The investigation identified that the ATC controller's lack of experience may have contributed to the incident, specifically regarding the issuance of an expedite instruction to a heavy aircraft in a climb phase near its maximum altitude. While the crew attempted to comply, the rapid increase in climb rate led to a loss of kinetic energy, forcing the crew to reduce the climb rate to regain airspeed.
- A significant contributing factor was the lack of proper communication between the flight crew and ATC, as the crew did not inform the controller that the climb rate had been reduced due to aircraft performance limitations.
- The ATC instruction to change course was determined to be a standard operational procedure to maintain separation once the altitude deviation was detected.